1. Field of the Invention
The present invention relates to cathode-ray tubes having a color-selecting electrode. More particularly, the present invention relates to a cathode-ray tube in which misalignment between a color-selecting electrode and a fluorescent glass panel is reduced to thereby minimize misregistration of colors, and which has improved resistance to impact, e.g., drop impact.
2. Description of the Related Art
In a typical color cathode-ray tube, three electron beams corresponding to three primary color signals, for example, which are emitted from respective cathodes, are arranged to land on fluorescent materials formed on the inner side of a fluorescent glass panel, thereby allowing the fluorescent materials to emit light of the primary colors.
Accordingly, an error in landing of the electron beams on the fluorescent materials causes misregistration of colors. To minimize the color misregistration, an arrangement has heretofore been adopted in which the area between the fluorescent materials (phosphors) for the respective colors on the fluorescent screen is filled with carbon, which is a black, non-luminescent substance. The coating of carbon gives some allowance for electron beam landing and hence makes it possible to minimize the color misregistration and improve the color picture quality.
FIG. 1 is a perspective view of a cathode-ray tube having a color-selecting mechanism known as "aperture grille", i.e., what is known as the Trinitron (trade name) cathode-ray tube. As is well known, the cathode-ray tube shown in FIG. 1 is composed of the following constituent elements: an aperture grille (AG) 13 of vertical slots; a color-selecting electrode having a pair of upper and lower frame members (A-members) 8 that constitute an AG frame for supporting the aperture grille 13 and a pair of left and right frame members (B-members) 9 that also constitute the AG frame; a fluorescent glass panel 1 formed with fluorescent stripes; and a funnel 4 having an electron gun 3 sealed therein. The fluorescent glass panel 1 and the funnel 4 are integrated into one unit through a frit seal portion 10.
To secure the color-selecting electrode 2 to the fluorescent glass panel 1, fixing pins 5 are formed on the fluorescent glass panel 1, as shown in FIG. 2, which is a perspective view of the color-selecting electrode 2. On the other hand, spring holders 6 are welded to the side surfaces of the AG frame A-members 8 at respective positions close to the fixing pins 5, and springs 7 having openings are welded to the spring holders 6, respectively. The fixing pins 5 are fitted into the respective openings of the springs 7.
There are two known methods of securing the color-selecting electrode 2 to the fluorescent glass panel 1, that is, a 3-pin system and a 4-pin system, which are classified by the number of fixing pins 5 used.
FIG. 3(a) shows a 3-pin type fixing method wherein the color-selecting electrode 2 is secured at three positions on the fluorescent glass panel 1, that is, a pair of left and right end portions B and C, and a lower end portion A. The color-selecting electrode 2 is secured to the fluorescent glass panel 1 by fitting fixing pins 5 disposed at these three positions into the corresponding springs 7.
FIG. 3(b) shows a 4-pin, windmill type fixing method wherein fixing pins 5 are disposed at a total of four positions A, B, C and D, respectively, which are set on a pair of left and right end portions and a pair of upper and lower end portions of the fluorescent glass panel 1, and the color-selecting electrode 2 is secured to the fluorescent glass panel 1 by fitting the fixing pins 5 into the corresponding springs 7 in such a state that the springs 7 are disposed to face clockwise or counterclockwise like the vanes of a windmill.
FIG. 4 shows a 4-pin (3+1) type fixing method wherein fixing pins 5 are disposed at four positions A, B, C and D, respectively, on a pair of upper and lower end portions and a pair of left and right end portions of the fluorescent glass panel 1.
Carbon stripes and fluorescent stripes are formed on the fluorescent glass panel 1 as follows: With the color-selecting electrode 2 removed from the fluorescent glass panel 1, a carbon or fluorescent slurry containing a photosensitive material is coated on the inner surface of the fluorescent glass panel 1, and thereafter, exposure is carried out with the color-selecting electrode 2 secured to the fluorescent glass panel 1. This process is carried out for each of the fluorescent materials for the chosen primary colors. Thus, the fluorescent stripes for each color and the corresponding carbon stripes are formed by repeating the operation of attaching the color-selecting electrode 2 to the fluorescent glass panel 1 and detaching the former from the latter.
If the relative position of the fluorescent glass panel 1 and the color-selecting electrode 2 shifts when fluorescent stripes of a particular color are to be formed after carbon stripes have been formed, the allowance for electron beam landing decreases.
If the relative position of the fluorescent glass panel 1 and the color-selecting electrode 2 shifts after carbon stripes and fluorescent stripes of each color have been formed, the electron beam center offsets from the fluorescent stripe center. If the amount of offset increases and the shift of the relative position of the carbon stripes and the fluorescent stripes increases, a color which is different from a desired color is emitted. Thus, misregistration of colors occurs.
The relative position of the fluorescent glass panel 1 and the color-selecting electrode 2 depends on the accuracy of the attaching and detaching operation carried out during the fluorescent stripe forming process. It may also be changed by thermal deformation of the color-selecting electrode 2 during a thermal process, e.g., a frit seal process, an evacuation process, etc., which is carried out after the formation of the fluorescent material. If the shift of the relative position of the fluorescent glass panel 1 and the color-selecting electrode 2 is large, the completed cathode-ray tube suffers from the failure (color misregistration) due to the fact that the electron beam landing position shifts from the center of the target fluorescent stripes to a considerable extent.
The relative position of the fluorescent glass panel 1 and the color-selecting electrode 2 may also shift due to acceleration acting on the color-selecting electrode 2 when a drop impact is applied to the cathode-ray tube, for example, during transport after shipment. Accordingly, color misregistration occurring during the delivery of the products also gives rise to a problem.